Abstract: On November 17, 2008, Employee #1 and his supervisor were assigned to perform pool maintenance work at a residential property located in Danville, CA. After Employee #1 shut off the power supply to the pool pump and turned off four water valves (three pool strainer valves and one spa strainer valve), the supervisor removed the cap from filter canister #2. Following that, Employee #1 and his supervisor cleaned the three pool strainers and the one spa strainer. The supervisor screwed the filter cover back on, opened the four strainer valves, and turned on the pool power supply. About 20 seconds later, the top cover of the filter blew off, hitting Employee #1, who was standing above filter canister #2. He sustained fractures to both arms and to both hands. He was taken to the John Muir Medical Center at Walnut Creek, CA, where he was hospitalized.